Is there a way I can display live/real time webcam video in the Motion Tracker?
Unfortunately no. It may be possible to stream video in using a codec module via python however the tracking markers likely couldn’t reliably keep up at a standard frame rate for a 720p+ so you would be limited to tracking sub HD resolutions and/or suffer delay/stuttering. Tracking via proxy and putting track over full resolution might work but would incur accuracy errors and be harder to track. There are programs designed specifically for real time tracking which you would be much better off using than Blender. 

Also don’t forget that even if you managed real time tracking the best graphics quality you could achieve is GLSL render or BGE. Unless you are a shader code expert you would be quite limited by this. Though not terrible certainly a step down from other rendering options.

If you are into coding and want to find a non standard solution to this problem you could do a search for a real time tracking module and stream it your video and enter the resulting track data into a more capable game engine... But it would be a lot of work, certainly not the easy and Blenderish way your asking for :(